Three-dimensional objects generated by an additive manufacturing process may be formed in a layer-by-layer manner. In one example of additive manufacturing, an object is generated by solidifying portions of layers of build material. In examples, the build material may be in the form of a powder, fluid or sheet material.
In some such processes, energy may be applied to a build material. For example, energy may be applied to preheat the build material to a temperature which is close to its melting point. Energy may also be applied to cause melting, so that regions of the build material may fuse to form portions of an object.